1. Field of the Invention
The present invention relates to a lens barrel which can be used as a photographing lens barrel of a camera.
2. Description of the Related Art
As an example of a conventional lens barrel in which a movable lens group provided in the lens barrel is moved in an optical axis direction to vary an axial position of the movable lens group, a lens barrel which is provided with a rotatable ring and a cam ring which is driven to rotate about the optical axis while moving in the optical axis via rotation of the rotatable ring is known in the art. A set of follower pins formed on a support frame of the movable lens group are respectively engaged in a corresponding set of cam grooves formed on the cam ring so that the cam ring rotates about the optical axis while moving forward in the optical axis direction by rotation of the rotatable ring and so that the movable lens group moves forward in the optical axis direction relative to the cam ring by rotation of the cam ring.
Moving the cam ring in the optical axis direction while moving the movable lens group in the same direction relative to the cam ring in such a manner can achieve a large amount of movement of the movable lens group in the optical axis direction, and therefore makes it possible to achieve a high zoom ratio if the lens barrel is a zoom lens barrel, in which the focal length can be varied continuously.
However, if this type of lens barrel is used as a photographing lens of a camera, when moving forward in the optical axis direction, the cam ring projects forward from the front wall of the camera to be exposed to the outside, so that the outward appearance of the lens barrel deteriorates. This is especially prominent if the lens barrel is an extendable (telescoping) type of zoom lens barrel since the amount of forward movement of the cam ring is generally large.
In addition, if the cam ring projects forward from the camera body to be exposed to the outside, the cam ring is subject to external forces directly applied thereto, which may make it impossible to move the movable lens group linearly in the optical axis direction with precision.
A conventional lens barrel having a structure wherein a cam ring which is driven to rotate about the optical axis and is provided with a set of cam grooves so that a set of follower pins formed on a support frame of the movable lens group are respectively engaged in the set of cam grooves of the cam ring, and further wherein a linear guide ring having a set of linear guide grooves for guiding the set of follower pins of the lens support frame linearly in the optical axis direction is provided between the cam ring and the movable lens group so that the movable lens group moves in the optical axis direction by rotation of the cam ring relative to the linear guide ring, is known in the art.
However, providing such a linear guide ring between the cam ring and the movable lens group increases the diameter of the cam ring. As a consequence, the diameter of the lens barrel increases.
Moreover, if an external force is applied to an outer peripheral surface of an exterior element of the lens barrel, the external force may exert a harmful effect on the movement of the movable lens group if transferred thereto. Therefore, adopting such a structure of the lens barrel is not desirable.
As an example of a conventional lens barrel in which a movable lens group positioned in the lens barrel is moved in an optical axis direction, a lens barrel having a cam ring driven to rotate about the optical axis wherein a set of follower pins fixed to the lens group are respectively engaged in a corresponding set of cam grooves on the cam ring to be guided linearly in the optical axis direction so that the movable lens group moves in the optical axis direction by rotation of the cam ring is known in the art.
In the case of moving the movable lens group in the optical axis direction by engagement of the set of cam grooves with the set of follower pins, clearances are arranged for the follower pins in the cam grooves to ensure the smooth movement of the follower pins in the cam grooves. Therefore, backlash occurs between the follower pins and the cam grooves when the movable lens groove moves, which deteriorates the performance of the focusing system. Moreover, in the case of moving a ring member, an outer peripheral surface of which serves as an exterior surface of the lens barrel in the optical axis direction, by a cam mechanism provided in the lens barrel which includes a set of follower pins formed on the ring member and a corresponding set of cam grooves formed on a cam ring, backlash occurs between the ring member and the cam ring.
Furthermore, as an example of a lens barrel, a lens barrel which is provided with a cam ring driven to rotate about the optical axis while moving in the optical axis, and a ring member positioned around the cam ring to serve as an exterior component of the lens barrel, is known in the art. A set of follower pins formed on the ring member are respectively engaged in a corresponding set of cam grooves formed on the cam ring so that the cam ring moves in the optical axis direction together with the ring member by rotation of the cam ring.
However, the ring member is subject to external forces directly applied thereto since the ring member serves as an exterior component of the lens barrel. If a large external force is applied to the ring member, the external force is transferred to the cam ring via the follower pins of the ring member to thereby deform the cam ring to the extent that one or more of the follower pins may come off the associated cam grooves, and in a severe case, the cam ring may even be damaged. To prevent this problem from occurring, the wall thickness of the cam ring can be increased and/or the cam ring can be made out of a high stiffness material for the purpose of increasing the strength of the cam ring. However, the cam ring becomes large and heavy if the wall thickness of the cam ring is increased, and the material cost and also the machining cost increase if the cam ring is made of a high stiffness material.
The present invention provides an extendable lens barrel in which a movable lens group can move in an optical axis direction by a large amount without exposing the exterior surface of the cam ring to the outside of the lens barrel when the lens barrel is extended forward. The present invention further provides a lens barrel in which a movable lens group moves in an optical axis direction with the use of a combination of a cam ring and a linear guide member, wherein the diameter of the lens barrel can be reduced and no external force is transferred to a movable lens group, even if an external force is applied to an exterior component of the lens barrel, while ensuring smooth movement of the movable lens group, wherein no backlash occurs between a movable lens group and a cam ring and between the cam ring and a ring member, which serves as an exterior component of the lens barrel, when the movable lens group and the ring member are moved in the optical axis direction, and/or wherein a cam ring is not deformed even if a large external force is applied to a ring member which serves as an exterior component of the lens barrel.
For example, in an embodiment of the present invention, a lens barrel is provided, including a cam ring which rotates about an optical axis while moving in the optical axis direction, the cam ring including at least one cam groove formed on an inner peripheral surface thereof; a movable lens frame supported by the cam ring and provided inside the cam ring, the movable lens frame being movable in the optical axis direction without rotating about the optical axis; a cam mechanism for moving the movable lens frame in the optical axis direction by an amount of movement greater than an amount of movement of the cam ring in the optical axis direction via rotation of the cam ring in accordance with a profile of the cam groove; and an outer ring which is provided around the cam ring and is engaged with the cam ring so that the cam ring is rotatable about the optical axis relative to the outer ring and so that the outer ring moves together with the cam ring in the optical axis direction.
The cam ring can further include at least one second cam groove formed on an outer peripheral surface of the cam ring, the lens barrel further including an inner ring provided between the cam ring and the outer ring, the inner ring being guided linearly in the optical axis direction without rotating about the optical axis; and a second cam mechanism for moving the inner ring in the optical axis direction by the rotation of the cam ring in accordance with a profile of the second cam groove.
It is desirable for the profile of the cam groove which is used to move the movable lens frame in the optical axis direction to be substantially the same the profile of the second cam groove which is used to move the linearly movable ring in the optical axis direction.
The outer ring can include a main ring body made of synthetic resin; and a reinforcing ring fitted on the main ring body to be fixed thereto.
It is desirable for the inner ring to include a main ring body made of synthetic resin; and a reinforcing ring fitted on the main ring body to be fixed thereto.
The lens barrel can be a zoom lens barrel, the movable lens frame supporting at least one lens element of a zoom lens optical system provided in the zoom lens barrel.
It is desirable for the reinforcing ring to be made of metal.
It is desirable for the outer ring to be guided linearly in the optical axis direction without rotating about the optical axis.
The lens barrel can further include a stationary ring, the cam ring being positioned inside the stationary ring, and the movable lens frame being movable in the optical axis direction without rotating about the optical axis relative to the stationary barrel.
In another embodiment, a lens barrel is provided, including a stationary ring; a cam ring provided inside the stationary ring and driven to rotate about an optical axis; a linear guide ring positioned between the stationary ring and the cam ring, the linear guide ring being guided linearly in the optical axis direction without rotating about the optical axis via the cam ring; and a movable lens frame provided inside the cam ring to move in the optical axis direction via rotation of the cam ring. The linear guide ring includes a lens frame support portion provided with the linear guide ring, the lens frame support portion being located before a front end of the movable lens frame. The movable lens frame is guided by the lens frame support portion in the optical axis direction without rotating about the optical axis.
The movable lens frame can include a front movable lens frame guided linearly in the optical axis direction without rotating about the optical axis via the frame support portion to be supported thereby.
The lens barrel can further include a linear guide mechanism, provided between the front movable lens frame and the linear guide ring, for guiding the front movable lens frame in the optical axis direction, the linear guide mechanism including at least one linear guide boss which extends rearward from the lens frame support portion; and at least one linear guide hole, formed on the front movable lens frame, in which the linear guide boss is engaged to be slidable therein.
The movable lens frame can further include a rear movable lens frame which is supported by the front movable lens frame, the rear movable lens frame being guided linearly in the optical axis direction without rotating about the optical axis via the front movable lens frame.
The linear guide boss can include a set of three linear guide bosses formed on the lens frame support portion at equi-angular intervals in a circumferential direction about the optical axis, and the linear guide hole includes a set of three linear guide holes in which the set of three linear guide bosses are slidably engaged, respectively.
Each of the set of three linear guide holes can be formed to have an oval cross section.
The lens barrel can be a zoom lens barrel, wherein the movable lens frame supports at least one lens element of a zoom lens optical system provided in the zoom lens barrel.
In another embodiment, a lens barrel is provided, including a cam ring which rotates about an optical axis while moving in the optical axis direction, the cam ring including at least one first cam groove and at least one second cam groove; a movable lens frame supported by the cam ring to be movable in the optical axis direction without rotating about the optical axis; a first cam mechanism for moving the movable lens frame in the optical axis direction by rotation of the cam ring in accordance with a profile of the first cam groove; a linearly movable ring supported by the cam ring to be movable in the optical axis direction without rotating about the optical axis; a second cam mechanism for moving the linearly movable ring in the optical axis direction by the rotation of the cam ring in accordance with a profile of the second cam groove; and a biasing device which biases the movable lens frame and the linearly movable ring in opposite directions in the optical axis direction.
It is desirable for a profile of a portion of the first cam groove which is used to move the movable lens frame in the optical axis direction to be substantially the same as a profile of a portion of the second cam groove which is used to move the linearly movable ring in the optical axis direction.
The movable lens frame and the linearly movable ring can be provided inside and outside the cam ring, respectively.
The lens barrel can be a zoom lens barrel, the movable lens frame supporting at least one lens element of a zoom lens optical system provided in the zoom lens barrel.
In another embodiment, a lens barrel is provided, including a cam ring which rotates about an optical axis while moving in a direction of the optical axis; a movable lens frame supported by the cam ring to be positioned inside the cam ring and to be movable in the optical axis direction without rotating about the optical axis; a first cam mechanism including at least one first cam groove formed on the cam ring and at least one first cam follower formed on the movable lens frame to be engaged in the first cam groove, the first cam mechanism moving the movable lens frame in the optical axis direction via rotation of the cam ring due to engagement of the first cam groove with the first cam follower; a linearly movable ring supported by the cam ring to be provided outside the cam ring and to be movable in the optical axis direction without rotating about the optical axis; and a second cam mechanism including at least one second cam groove which is formed on the cam ring and at least one second cam follower formed on the linearly movable ring to be engaged in the second cam groove, said second cam mechanism moving the linearly movable ring in the optical axis direction by the rotation of the cam ring due to engagement of the second cam groove with the second cam follower. The first cam groove includes a portion having a profile which is substantially the same as a profile of the second cam groove, wherein the substantially same profile portions of the first and second cam grooves are formed at different positions in the optical axis direction. The first cam follower and the second cam follower are aligned on a line parallel to the optical axis.
The first cam mechanism can be formed on an inner peripheral surface of the cam ring, and the second cam mechanism can be formed on an outer peripheral surface of the cam ring.
The lens barrel can further include a biasing device which biases the movable lens frame and the linearly movable ring in opposite directions in the optical axis direction.
It is desirable for each of the first cam groove and the second cam groove to be formed as a bottomed cam groove.
The lens barrel can further include a stationary ring, the cam ring being provided inside the stationary ring and driven to rotate about the optical axis while moving in the optical axis direction relative to the stationary ring.
The lens barrel can be an extendable lens barrel.
The present disclosure relates to subject matter contained in Japanese Patent Applications Nos.2001-83264, 2001-83266, 2001-83267 and 2001-83682 (all filed on Mar. 22, 2001) which are expressly incorporated herein by reference in their entireties.